The present invention relates to an ink-jet printing method and an ink-jet printer of the type wherein the ink emerging through a nozzle of an ink drop generator breaks into a stream of ink drops which are selectively charged or not charged so as to steer them to a gutter or to a recording medium.
A typical example of the prior art ink-jet printing methods and ink-jet printers is such that ultrasonic vibration is transmitted to the pressurized ink confined in an ink manifold of an ink drop generator so that the ink jet emerging through a nozzle of the ink drop generator may break into a stream of ink drops equally spaced apart from each other. A charge electrode is disposed at a position where the ink jet breaks into drops and is charged with a charging voltage in response to the character or image forming signal in such a way that each ink drop may be charged independently of each other to a different level. The charged ink drops are deflected by a pair of deflection plates so that the characters or images of one line may be printed or recorded in one main scanning step. (For further reference, see Japanese Laid-Open Patent No. 50-60131). During the main scanning in for instance the transverse direction, one-line auxiliary scanning in the longitudinal direction is repeated while the level of the voltage applied to the charge electrode is varied. Therefore the formation of each ink drop must be precisely timed with the application of the voltage pulse to the charge electrode, but it is extremely difficult to attain the correct synchronization between the formation of each ink drop and the application of the voltage pulse to the charge electrode. Furthermore the printed image or character is caused to incline.
In the case of the ink-on-demand type ink-jet printing methods and printers, in response to the character or image forming signal or the ink-placement signal a voltage pulse is applied to an ultrasonic transducer mounted on an ink drop generator and one dot is placed on a recording paper. Therefore the synchronization between the formation of an ink drop and the application of a voltage pulse to the charge electrode will not present any serious problems. Furthermore the inclination of the printed character or image may be eliminated.
In the deflection type ink-jet printing methods and ink-jet printers, the voltage applied to the charge electrode is so controlled that the repetitive auxiliary or complementary scanning in the longitudinal direction may be eliminated and consequently the timing for applying the voltage to the charge electrode may have more degrees of freedom, but while one line is printed in one main scanning in the prior art printing method, a plurality of main scannings must be made (for instance, nine scannings when one line consists of nine picture elements). When a plurality of nozzles are disposed in an array, one line may be printed within one main scanning so that the printing speed may be increased. However the electrical connections, maintenance, inspection and especially cleaning of charge electrodes which are disposed for respective nozzles would become extremely difficult. For instance, in the case of the deflection type ink-jet printers, ink dribbling occurs because of the time lag in pressure transmission when the print head is energized or de-energized so that the contamination of the charge electrode and the deflection electrodes results. When a large number of charge electrodes are densely disposed, their cleaning becomes extremely difficult. The contamination of the charge and deflection electrodes results in mischarging and misdeflection of ink drops, thus resulting in drop misplacements and the contamination of the printing head and the recording medium.